I went ahead and pulled the outlet out to check it out. No ground wire as suspected. I went to Lowe's and picked up a new metal outlet box and a ground wire. I grounded the outlet to the box. It didn't eliminate the problem totally but did help quiet the amp noise a bit.
Of course not. That house prolly has the Paul Revere seal or electrical approval too, with the age of it. Remember him? He flew kites in lightning storms.
The wall box has to be grounded to
SOMEthing or it's still not a grounded circuit.
In the ol'
mud-n-wire-pair days where they just stuffed the wires IN the lathe before they plastered them over, and they only have a single pair and
there ain't no ground in that system at all.
For safety, you MAY have to run a new ground home-run to the distribution panel - or the worst case4 tie into a Eufer or another ground anode that you
might be able to pick up somewhere else.
DO NOT USE A WATER PIPE - especially in a very old house as the integrity of the joints are very suspect.
The Eufer isn't really Kosher either, but it may keep you from doing the 60-cycle slam in a puddle of your own juices on the floor awaiting someone to happen by who
maybe knows CPR.
You really need to get back to the d-box for a good ground.
DANGER, Will Robbins! DANGER!